Bubble Phenomena Research Articles

Visualization of Hydrogen Bubbles in Porous Transport Layer in Toluene Direct Electro-Hydrogenation Electrolyzer Using X-Ray CT System

Introduction Currently, the use of renewable energy is being promoted as an approach to decarbonization. However, renewable energy requires stable energy storage and supply because the amount of electricity is affected by time and climate. One of the solutions is use of hydrogen as an energy source. As the demand for hydrogen increases in the future, a large amount of hydrogen will be needed, and the storage and transportation of large amounts of hydrogen will also be necessary. However, the methods for storing and transporting large amounts of hydrogen have not yet been established, and this is one of the challenges in the current hydrogen utilization. One of the methods for storing and transporting large amounts of hydrogen is the organic hydride method. The organic hydride method is a method of storing and transporting hydrogen using hydrogenation and dehydrogenation of organic compounds. Among these, the use of toluene and methylcyclohexane (MCH) has attracted attention. The advantages of using toluene and MCH include the following: because toluene and MCH are liquids at normal temperature and pressure, they can be transported at about 1/500th the volume of direct hydrogen gas transport; toluene and MCH can be reused; hydrogenation and dehydrogenation are the only reactions, so no byproducts are generated; and they can be transported in the same way as petroleum. Hydrogen can be transported in the same way as petroleum. Therefore, it is expected to be used as a storage and transport medium for hydrogen.A toluene direct electro hydrogenation electrolyzer is available as a means of hydrogenating toluene. In the toluene direct electro hydrogenation electrolyzer, hydrogen and toluene are supplied to the electrolyzer, and electricity is applied to protonate the hydrogen and supply it to toluene to produce MCH. The advantages are that cost and time losses can be reduced because water electrolysis and toluene hydrogenation can be performed simultaneously, there is no heat loss in the reaction, and the theoretical decomposition voltage can be reduced compared to electrolysis of water and hydrogenation of toluene separately. However, during hydrogenation of toluene, a part of the water being electrolyzed is transferred to the toluene reaction surface, reducing the reaction efficiency to MCH. In addition, part of the protonated hydrogen becomes hydrogen bubbles, which inhibit the fuel supply and reduce the reaction area. Furthermore, the phenomena of water movement and hydrogen bubbles in toluene hydrogenation have not yet been studied.In this study , we aim to understand the generation of hydrogen bubbles by visualizing the phenomena in toluene hydrogenation using a toluene direct electro hydrogenation electrolyzer with an X-ray CT system, and to provide a guideline for future research on the suppression of hydrogen bubble generation and water movement. Fig. 1 shows a schematic diagram of the toluene direct electro- hydrogenation electrolyzer used in this experiment. The electrolyzer consists of a catalyst layer, a gas diffusion layer (GDL), and a separator, in that order. The electrolyzer is operated by supplying toluene to the anode side and hydrogen to the cathode side, and electricity is supplied. Visualization of the interface between the GDL and catalyst layer on the cathode side of the electrolyzer during operation using an X-ray CT system allows the phenomena on the reaction surface to be visualized. Figure 2 Visualization of the inside of the electrolyzer during operation. Fig. 2 (a) shows the electrolyzer filled with MCH and (b) shows the electrolyzer filled with toluene. The toluene electrolyzer generates fewer hydrogen bubbles, which confirms that the reaction is normal, and the correlation between the current density and the generation of hydrogen bubbles is examined. Figure 1

Equatorial Plasma Bubbles: A Review

The equatorial plasma bubble (EPB) phenomenon is an important component of space weather as the ionospheric irregularities that develop within EPBs can have major detrimental effects on the operation of satellite-based communication and navigation systems. Although the name suggests that EPBs occur in the equatorial ionosphere, the nature of the plasma instability that gives rise to EPBs is such that the bubbles may extend over a large part of the global ionosphere between geomagnetic latitudes of approximately ±15°. The scientific challenge continues to be to understand the day-to-day variability in the occurrence and characteristics of EPBs, such as their latitudinal extent and the development of irregularities within EPBs. In this paper, basic theoretical aspects of the plasma processes involved in the generation of EPBs, associated ionospheric irregularities, and observations of their characteristics using different techniques will be reviewed. Special focus will be given to observations of scintillations produced by the scattering of VHF and higher frequency radio waves while they propagate through ionospheric irregularities associated with EPBs, as these observations have revealed new information about the non-linear development of Rayleigh–Taylor instability in equatorial ionospheric plasma, which is the genesis of EPBs.

Turning Filter Bubbles into Bubblesphere with Multi‐Viewpoint KOS and Diverse Similarity

ABSTRACTThe filter bubble phenomenon and its negative societal effects have been extensively explored in the literature in the past decade. However, the ability of modern AI‐based systems to create personalized information bubbles, that is, to classify similar contents and users into clusters according to their interests and behavior, can actually be quite beneficial if utilized and managed properly and ethically. In this article we present ongoing research that aims to refine such bubble‐building smart systems by adopting an ethical, multi‐perspective approach that allows for linking isolated bubbles into a consolidated bubblesphere and offering users a choice to explore diverse bubbles related to their topics of interest. To implement the proposed approach, content matching should be based on diverse similarity, which can be derived from a multi‐viewpoint KOS. In addition, the study explores how such a multi‐viewpoint KOS and bubblesphere can be constructed using Wikidata's ranks and qualifiers.

A visualized investigation of bubble breakup in a swirl‐venturi bubble generator

AbstractThe dynamics and breakup of bubbles in swirl‐venturi bubble generator (SVBG) are explored in this work. The three‐dimensional movement process and breakup phenomena of bubbles are captured by one high‐speed camera system with two cameras while the distribution of swirling flow field is recorded through Particle Image Velocimetry technology. It is revealed that bubbles have two motion trajectories, which are deeply related to bubble breakup. One trajectory is that mother bubble moves upward in an axial direction of the SVBG to the diverging section, and the other trajectory is that mother bubble rotates obliquely upward to another side‐wall along the radial direction. Meanwhile, binary breakup, shear‐off‐induced breakup, static erosive breakup, and dynamic erosive breakup are observed. For relatively high liquid Reynolds number, vortex flow regions are extended and the bubble size is reduced. Furthermore, it is worth noting that the number of microbubbles increases significantly for intensive swirling flow.

Novel laboratory extraction method using magnetically micro bubble stream

Innovative, sensitive and accurate method for liquid-liquid extraction using bubble phenomenon. is presented in this work. A working system was designed, consisting of two basic parts: the pump air to generate the bubbles and the pump device, to pump or withdraw the organic layer from the liquid-liquid system key variables study was performed in the system containg Dithizone (0.001 M) in CHCl₃ solvent and aqueous copper (II) chloride (1000 ppm) solution to find out the extent of their impact on the extraction performance obtained in this way. The effect of copper concentration in the initial sample, shake time, size of bubbles flowrate were studied, fixing the optimal conditions: for a sample of (10 mL) aqueous solution of Cu (II) chloride, the optimum copper (II) concentration in the analyzed sample is (0.0001M) , the size of bubbles 2.6 L\min, the shaking time is (15 min), and the pump flowrate is ( 50sec/mL). In these optimum conditions, the extraction degree was (91.1 %). The results of the innovative bubbles extraction method were compared with previous studies, and found they were more efficient than the classical methods of extraction using funnel separation and multiple extraction.

Developing high intensity ultrasonic cleaning (HIUC) for post-processing additively manufactured metal components

The high energy phenomenon of cavitation bubble collapses has enabled numerous applications, including cleaning. In ultrasonic cleaning, cavitation intensity is typically lower than in other applications, such as sonochemistry and material processing. However, there has been an emerging application in intense cleaning of metal additively manufactured (AM) components. The presence of partially melted powders on AM surfaces is undesirable, contributing to high surface roughness and posing contamination risks during usage. We designed a high-intensity cavitation cleaning process that has significantly higher inertial cavitation intensity – i.e., erosion potential – than a conventional ultrasonic cleaning tank. Through acoustic signal characterisation, we showed that placing transducer sets on four sides of the tank could effectively focus and generate high-amplitude pressure waves directed towards the central region. Strong subharmonic signals indicate intensely inertial cavitation throughout the tank. Cavitation intensities were measured at various locations to understand the wave transmission characteristics and distribution patterns. Our results show that the cavitation intensity distribution is highly dependent on the height position. Finally, we demonstrated that the high intensity ultrasonic cleaning (HIUC) process could remove partially melted powders from an AM surface – which was not possible through conventional ultrasonic cleaning. HIUC could lead to higher cleaning efficiency and enhanced AM specimen cleanliness.

Sentiment, Google queries and explosivity in the cryptocurrency market

The lack of fundamental values in the cryptocurrency market paves the way for the rise of unprecedented speculative bubble phenomena, which are often associated with alternating phases of investors’ fear and greed. We propose exploiting the information derived from a large set of cryptocurrency news and Google Search Indices to detect and, possibly, anticipate the presence of speculative bubbles in cryptocurrency prices. This is done using a Backward Superior Covariate-Augmented Dickey–Fuller (BSCADF) test, which allows us to explicitly account for market sentiment when testing the presence of an explosive root in cryptocurrency prices. Our results show that the covariate test statistics does significantly diverge from the traditional statistics in concomitance with price surges, highlighting the ability of sentiment to predict speculative bubble occurrences. We also show how a polarised version of investors’ sentiment plays an overall more determinant role, if compared to news volume and Google queries, in providing an early warning signal of market bubble episodes in cryptocurrencies.

Bubble growth in water vortex unit and its effect on suction force

The vortex unit is a non-contact negative pressure generating mechanism. It blows high-pressure fluid tangentially into a cylindrical chamber through several nozzles to form a swirling flow and relies on the centrifugal inertial effect of the swirling flow to generate negative pressure and suction force. To date, all related studies and applications have used compressed air as the working fluid. Because the density of water is much greater than that of air, in this study, water was used as the working fluid to greatly improve the centrifugal inertial effect of the swirling flow. Based on this innovative idea, the swirling flow of the vortex unit with water as the working fluid was investigated through experiments. A convergence-growth-stabilization phenomenon of bubbles was discovered, and the effect of the converged central bubble on the central pressure and suction force was elucidated. The mechanism of the gap height and flow rate on the converged central bubble and suction force was also studied. The reason for the formation of the converged central bubble is that the negative pressure causes the gas to evolve out of the water, and the dispersed tiny bubbles move to the center of the vortex chamber under the influence of centrifugal inertia to form a large bubble. This study provides new research directions and usages of the vortex unit and provides important basic knowledge for further research.

Cognitive Dissonance pada Konteks Berkomunikasi dan Mencari Informasi di Ruang Digital: Fenomena Selective Exposure

In the digital space that is now increasingly dominating our lives, there are challenges and new social situations that require us to adapt. Cognitive Dissonance Theory (CDT) places a focus on seeing human behavior in situations that are incompatible with the cognition he has. After six decades of CDT's existence, there have been many derivative concepts that can be used to analyze causation in this dissonance situation. Selective exposure is a concept derived from CDT that has received attention from researchers in analyzing the phenomenon of filter bubbles and echo chambers. To examine the application of CDT in a contemporary context, in this digital space, this study was conducted by making a literature review that focuses on elaborating on the theory and context of CDT in use. Using qualitative content analysis from a collection of previous studies, this study maps the relevance of theory to the context of situations in the digital space. The conclusion is that CDT, both based on basic assumptions and derived concepts tested by other researchers, can objectively predict the cause-and-effect of a situation that triggers dissonance in a person's cognition when a situation with similar conditions occurs.

Surface effects on Sub-cooled pool boiling for smooth and laser-ablated silicon surfaces

Smooth and laser-ablated silicon surfaces with wettability ranging from SHI (super-hydrophilic) to SHO (super-hydrophobic) are tested in subcooled pool boiling of water. The experiment focuses on the observation of bubble phenomena using a high-speed camera and the measurement of surface temperature using an infrared camera. The formation and departure of vapor bubbles from the surfaces are found to vary significantly with the surface wettability. Nucleate boiling curves show that both the heat transfer coefficient and the critical heat flux increase with the surface wettability changing from SHO to SHI. For the hydrophilic surfaces (smooth and textured), the heat transfer coefficient increases with the heat flux. For the hydrophobic surfaces (smooth and textured), the heat transfer coefficient decreases with the increasing heat flux. The effect of the surface wettability is quantitatively assessed using the surface-fluid factor. It is found that the factor's value increases with the surface wettability changing from SHI to SHO. The surface effect for the hydrophilic surfaces remains relatively constant over the nucleate boiling range, whereas for the hydrophobic surfaces the effect shows significant dependency on the heat flux. These findings are also revealed from the boiling tests on a biphilic surface consisting of a SHO region and a SHI region.

Numerical study on gas–liquid two phase flow characteristic of multistage electrical submersible pump by using a novel multiple-size group (MUSIG) model

Electrical submersible pumps (ESPs) face enormous challenges in the petroleum industry while handling gas–liquid two-phase flow. The major difficulty is caused by the accumulation of gas bubbles inside ESP-impellers, which results in mild to severe degradation in pump performance. Therefore, to analyze the influence of gas entrainment and bubble size, a combination of experimental and numerical analysis is performed on a five-stage mixed-flow ESP in the present study. The experiments are first conducted to analyze the performance of ESP under pure water conditions at different rotating speeds, followed by the gas–liquid two-phase flow experiments that are performed at constant rotating speed (1475 r/min) and for a wide range of inlet gas void fractions (IGVFs). For numerical calculations, a novel multiple-size group (MUSIG) model is applied in ANSYS CFX to analyze the performance and different flow patterns in ESP in different IGVFs and understand the coalescence and breakup phenomena of gas bubbles in the impeller flow passage. The simulation results from the MUSIG model are compared with the Euler–Euler two-fluid model and test results. The MUSIG model can more accurately predict the changes in the performance and internal flow-field of ESP under two-phase flow conditions. Moreover, when the MUSIG model is used to calculate the two-phase flow of the ESP, the first-stage impeller has a higher head than other stages because the flow inside the second and other stages is affected by the disoriented flow coming from the first-stage diffuser and other return channels. Furthermore, this study gives an insight into the comprehensive application of the novel MUSIG model for complex turbo-machine designs such as ESP.

Effects of Thermally Induced Bubbles on the Discharge Characteristics of Oil-Impregnated Pressboard

Under temperature and moisture combined, bubbles will be formed in oil-impregnated paper/pressboard (OIP/OIPB). Although many studies have been done to understand the thermo-induced bubble phenomenon in OIPB, the formation mechanism is not, let alone its effect on discharge characteristics and insulation performance of OIPB. In this article, the phenomena and mechanisms of thermally induced bubbles, their effects and mechanisms on the partial discharge (PD), and breakdown characteristics of OIPB are investigated. The results show that the bubble inception temperature (BIT) decreases significantly with the increase of the moisture of OIPB. There is a growth process of bubbles from small to large, and the heating temperature and moisture content of OIPB affect the gas component inside the bubble. Thermal bubbles significantly reduce the PD inception voltage (PDIV) and breakdown voltage (BV), and the PD evolution and dissolved gas components in the oil show significant differences in the presence/absence of bubbles. Interestingly, PDIV and BV start to decrease in a temperature interval before BIT, and we infer that many microbubbles and gaseous channels exist inside OIPB before observable bubbles are formed on the surface. Considering the fibrous porous structure of OIPB and combining it with the bubble nucleation theory, we propose a new model for interpreting bubble formation and insulation degradation. The model suggests that bubbles (vapors) form first in microcavities and holes inside the OIPB and then spill over to the surface to form observable bubbles. The microcavities and pores in the OIPB are filled with gas (vapor) as the main cause of PD inception and insulation degradation. This study contributes to understanding the mechanisms of bubble formation in oil–paper insulation as well as provides a reference for risk assessment during overload operation and diagnosis of bubble-induced related faults of transformers.

A tough, elastic ion gel with adaptive interface for high performance and safe lithium metal anodes

Lithium metal batteries (LMBs) with high energy densities are highly desirable for energy storage. However, they suffer from the low Columbic efficiency (CE) because of the continuous breaking of solid electrolyte interphase (SEI) and formation of dead lithium generated from the infinite volumetric changes of lithium metal anodes. Herein, a tough and elastic gel electrolyte is designed to create a dynamic interface between lithium metal and gels to tackle this grand challenge. A stable cycling of lithium metal anodes is achieved with a high CE of 99.3% for 1000 cycles and ultralong cycle life of 2,000 h, with traditional ether electrolytes. In-situ optical microscopy insights into the interfacial evolution of the lithium electrode employing gel as electrolyte reveals the uniform Li plating/stripping behavior and the eliminated bubble phenomenon observed in Celgard system, yielding in-depth comprehensions of the precipitation mechanism and interfacial establishment in gel-based LMBs.

The identification of spatial bubbles in a real estate market

There is great interest in identifying and modelling real estate market bubbles over time. However, the spatial dimension of those bubbles gets less attention. While building on the theory of real estate market equilibrium and formation of market bubbles, this research focuses on the spatial bubbles of the market value of apartments inside a city. This approach adds another dimension to the phenomena of real estate market bubbles. The scientific problem of this study is whether the spatial differentiation of real estate encourages the formation of spatial bubbles in real estate market. The object of research is the spatial bubbles in real estate market. The aim of research is to identify the impact of spatial bubbles on real estate market value. Because of the nature of real estate market, the supply and demand of real estate does not match, therefore real estate almost never reaches the equilibrium market value and bubbles appear. The main idea behind this research is that the supply and demand equilibrium model can be applied not only to the changes over time but also across space inside a city. The spatial bubbles appear because of unexplained variance. The empirical research focuses on unexplained variance across space of market value of homogeneous apartments in two major cities in Lithuania. The prominent variance is eliminated through careful selection of projects and control variables such as floor and size of an apartment, distance to civic points and location. Up to 39% of unexplained variance of apartment market value across space was found when looking at 3D diagrams of residualised apartment market value of the selected cities. The main reasons behind formation of those spatial bubbles should be addressed by further research for deeper understanding of the phenomenon of spatial bubble formation.

A Biomimetic Human Lung-on-a-Chip with Colorful Display of Microphysiological Breath.

Lung-on-a-chip models hold great promise for disease modeling and drug screening. Herein, inspired by the iridescence phenomenon of soap bubbles, a novel biomimetic 3D microphysiological lung-on-a-chip system with breathing visualization is presented. The system, with an array of pulmonary alveoli at the physiological scale, is constructed and coated with structural color materials. Cyclic deformation is induced by regular airflow, resembling the expansion and contraction of the alveoli during rhythmic breathing. As the deformation is accompanied with corresponding synchronous shifts in the structural color, the constructed system offers self-reporting of the cell mechanics and enables real-time monitoring of the cultivation process. Using this system, the dynamic relationships between the color atlas and disease symptoms, showing the essential role of mechanical stretching in the phenotypes of idiopathic pulmonary fibrosis, are investigated. These features make this human lung system ideal in biological study, disease monitoring, and drug discovery.

Experimental studies of bubble dynamics under a broken horizontal plate

This paper presents an experimental study on the pulsation characteristics of bubbles under a damaged boundary. Bubble phenomena in the fluid domain, such as bubble shape, pulsation period, water jet, and motion, are observed, and the influence of distance parameters on these phenomena is analyzed in detail with the help of high-speed photography technology. We also discuss the relationship between bubble pulsation, the water spike form, and characteristic parameters under different boundary conditions, such as different hole shapes. It is found that the broken boundary weakens the effect of the wall on bubble motion, while the shape and area of the hole exert noticeable effects on the water spike. In addition, the rising part of the free surface consisting of three parts, the water spike, water skirt I, and water skirt II, along with their evolutionary forms at the gas–liquid interface, are experimentally studied.

Detecting an Existence of Bubble Price in Indonesian Islamic Stock

<i>Purpose</i> –The implementation of the Islamic capital market in Indonesia applies the principles of Islamic capital participation that meets the principles of sharia i.e. non-bubble stock. Screening of Islamic companies through methods applied by authority agencies with certain prerequisites actually cannot avoid speculative actions that represent with bubble price. This research intended to detect the existence of bubble price in the Indonesian Islamic Stock Index. This very useful for society that the grouping of an asset was not enough to get an Islamic principe. The current model or tools to analyse and detect the existence of bubble, the application of those method in Islamic assets was not avalibale. In order to appropriate with Islamic principes, the Islamic assets are not allowed contain bubble. This paper introduce that those principes establish or not using this paper analysis. An econometrical model as well as an equation, according to monthly data, Indonesian Islamic Stock Index (IDXS) variable analysed by Right Tail Augmented Dickey Fuller (RTADF) approach. This tool very useful to detect and date-stamping of bubble with more accurately than other tools. The results shows that Indonesian Islamic stock market contain or existing the price of bubble, even Islamic stock with any prohibition and selective instrument can not avoid from bubble phenomenon. The stock may exhibit sharia value, but if the market play the role, so that these value may fallen away.

Observation and modulation of gas film and plasma behavior in electrolytic plasma hybrid etching of semiconductor material 4H–SiC

Micromachining or nanostructuring of SiC single-crystal is attempted by an electrolytic plasma hybrid etching (EPHE) method. Aiming to enhance the process precision and consistency, this study focuses on investigating the phenomena of bubble and plasma occurrence in EPHE with varying pulse conditions. It is found that a higher voltage results in more significant plasma and current and consequently a more evident etching of SiC. EPHE involves oxide layer formation on the SiC surface by plasma or thermal oxidation, which is easily broken under higher voltages and fluid hydrodynamic flow. Increasing the pulse frequency reduces the formed gas/plasma layer thickness, leading to an improved machining resolution. The plasma cannot be induced when the pulse duty ratio is reduced below a critical value due to the rapid dissipation of gaseous bubbles. However, excessive pulse duty ratio causes difficulty in renewing electrolytes, which induces anomalies like sparks. A compact plasma envelope with a minimum thickness is achieved with optimized pulse conditions, which enables micro-drilling of a Φ312 μm microhole with a small machining gap of 6 μm by EPHE using a Φ300 μm microrod electrode. The results demonstrate the feasibility of EPHE for micro-nano scale fabrication of SiC for related applications such as sensors and MEMS.

Memristive electromagnetic induction effects on Hopfield neural network

Due to the existence of membrane potential differences, the electromagnetic induction flows can be induced in the interconnected neurons of Hopfield neural network (HNN). To express the induction flows, this paper presents a unified memristive HNN model using hyperbolic-type memristors to link neurons. By employing theoretical analysis along with multiple numerical methods, we explore the electromagnetic induction effects on the memristive HNN with three neurons. Three cases are classified and discussed. When using one memristor to link two neurons bidirectionally, the coexisting bifurcation behaviors and extreme events are disclosed with respect to the memristor coupling strength. When using two memristors to link three neurons, the antimonotonicity phenomena of periodic and chaotic bubbles are yielded, and the initial-related extreme events are emerged. When using three memristors to link three neurons end to end, the extreme events owning prominent riddled basins of attraction are demonstrated. In addition, we develop the printed circuit board (PCB)-based hardware experiments by synthesizing the memristive HNN, and the experimental results well confirm the memristive electromagnetic induction effects. Certainly, the PCB-based implementation will benefit the integrated circuit design for large-scale Hopfield neural network in the future.

Acoustic and phase portrait analysis of leading-edge roughness element on laminar separation bubbles at low Reynolds number flow

Since laminar separation bubbles are neutrally shaped on the suction side of full-span wings in low Reynolds number flows, a roughness element can be used to improve the performance of micro aerial vehicles. The purpose of this article was to investigate the leading-edge roughness element’s effect and its location on upstream of the laminar separation bubble from phase portrait point of view. Therefore, passive control might have an acoustic side effect, especially when the bubble might burst and increase noise. Consequently, the effect of the leading-edge roughness element features on the bubble’s behavior is considered on the acoustic pressure field and the vortices behind the NASA-LS0417 cross-section. The consequences express that the distribution of roughness in the appropriate dimensions and location could contribute to increasing the performance of the airfoil and the interaction of vortices produced by roughness elements with shear layers on the suction side has increased the sound frequency in the relevant sound pressure level (SPL). The results have demonstrated that vortex shedding frequency was increased in the presence of roughness compared to the smooth airfoil. Also, more complexity of the phase portrait circuits was found, retrieved from velocity gradient limitation. Likewise, the highest SPL is related to the state where the separation bubble phenomenon is on the surface versus placing roughness elements on the leading edge leads to a negative amount of SPL.